Optical disk

ABSTRACT

An optical disk including concentric or spiral grooves, a first series of pits formed in the interrupted portions, and a second series of pits formed in portions of lands. Both of the first and second series of pits represent address information. The portions of the lands and the interrupted portions of the grooves are located in different radial directions. With this arrangement, even when the optical disk has a reduced track pitch, accurate address information is obtained, achieving a high-density recording optical disk.

FILED OF THE INVENTION

The present invention relates to optical disks, includingmagneto-optical disks, on which address information is prerecorded as aseries of pits.

BACKGROUND OF THE INVENTION

Among optical memories on/from which information is recorded/reproducedusing light, magneto-optical disks having a recording film made of aperpendicularly magnetized film as a recording medium have beenpractically used. Information is recorded on the magneto-optical diskswhen a direction of magnetization within light spots is arranged to beupward or downward by applying a magnetic field while irradiating laserlight onto the recording film.

As illustrated in FIG. 8, a magneto-optical disk has grooves 51. A lightspot 55 accurately follows a land 52 between the grooves 51. The addressinformation of a particular track that the light spot 55 follows isobtained because address information is recorded on each of the lands 52as pits 53.

Information is recorded on tracks as lands 52. The track pitch is almostequal to the diameter of the light spot 55 which is determined by thewavelength of laser light and the numerical aperture of an objectivelens. The objective lens converges the laser light into the light spot55. Usually, the wavelength of the laser light is between 780 nm and 830nm and the numerical aperture of the objective lens is between 0.45 and0.6. Thus, the light spot 55 has a diameter of between 1.2 and 1.4 μmand the track pitch is between 1.4 and 1.6 μm. Accordingly, the minimumdiameter of an upwardly or downwardly magnetized recording domain 54 isaround 0.8 μm.

A magneto-optical disk with flat mirrored sections 62 shown in FIG. 9 isalso well known. The mirrored sections 62 do not have grooves 61 butpits 63. The light spot 55 tracks the grooves 61, and the addressinformation of a particular track that the light spot 55 follows isobtained by reproducing the pits 63. Similar to the above-mentionedoptical disk of FIG. 8, the minimum diameter of a recording domain 64 onthe groove 61 of this magneto-optical disk is around 0.8 μm.

In recent years, magneto-optical disks including a recording film of amulti-layer structure have been produced so as to achieve magnetic superresolution effects. The magneto-optical disk with such a structureproduces a recording domain of a size much smaller than the size of thelight spot 55, achieving improved recording density. With the magneticsuper resolution technique, recording domains of size almost one half ofthe conventional size are stably formed. It is therefore possible toreduce the track pitch to around 0.8 μm or one half of the conventionaltrack pitch, improving the recording density significantly. For example,there is a detailed report on magnetic super resolution in "Journal ofJapanese Applied Magnetism Association", Vol. 15, No. 5, 1991, pp.838-845.

With the conventional structures, however, when the track pitch isreduced to a half, the size of the pit 53 is also reduced to a half,resulting in weaker signals from the pits 53.

Further, the distance between pits 53 formed on adjacent tracks is alsodecreased to a half. This causes crosstalk and prevents accurate addressinformation from being obtained.

SUMMARY OF THE INVENTION

An object of the present invention is to provide an optical disk whichhas a reduced track pitch and is capable of giving accurate addressinformation.

In order to achieve the above object, an optical disk of the presentinvention has concentric or spiral grooves, a first series of pitsformed in interrupted portions of the grooves, and a second series ofpits formed in portions of lands. Both of the first and second series ofpits represent address information. The portions of the lands and theinterrupted portions of the grooves are located in different radialdirections of the magneto-optical disk.

With this arrangement, it is possible to obtain accurate addressinformation even when the track pitch is reduced, thereby achieving ahigh-density recording optical disk.

For a fuller understanding of the nature and advantages of theinvention, reference should be made to the ensuing detailed descriptiontaken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1 through 7 illustrate embodiments of the present invention.

FIG. 1 is a view explaining a schematic structure of a magneto-opticaldisk according to a first embodiment.

FIG. 2 is a view explaining a schematic structure of a magneto-opticaldisk according to a second embodiment.

FIG. 3 is a view explaining a schematic structure of a magneto-opticaldisk according to a third embodiment.

FIGS. 4(a)-(f) are views explaining a process of making a master ofsubstrates for the magneto-optical disks shown in FIGS. 1 through 3.

FIG. 4(a) is a view explaining a first step of the process of making amaster.

FIG. 4(b) is a view explaining a second step of the process of making amaster.

FIG. 4(c) is a view explaining a third step of the process of making amaster.

FIG. 4(d) is a view explaining a fourth step of the process of making amaster.

FIG. 4(e) is a view explaining a fifth step of the process of making amaster.

FIG. 4(f) is a view explaining a sixth step of the process of making amaster.

FIG. 5 is a block diagram schematically illustrating a recording deviceused for the exposure of a photoresist during the process shown in FIGS.4(a)-(f).

FIGS. 6(a)-(c) are views explaining an exposure method of thephotoresist employed by the recording device of FIG. 5.

FIG. 6(a) is a view explaining a schematic structure of a substrate of amagneto-optical disk.

FIG. 6(b) is a view explaining the intensity of a light spot.

FIG. 6(c) is a view explaining the intensity of a light spot.

FIGS. 7(a)-(e) are views explaining another exposure method of thephotoresist employed by the recording device of FIG. 5.

FIG. 7(a) is a view explaining a schematic structure of a substrate of amagneto-optical disk.

FIG. 7(b) is a view explaining the intensity of a light spot.

FIG. 7(c) is a view explaining the intensity of a light spot.

FIG. 7(d) is a view explaining a voltage to be applied to a lightdeflector.

FIG. 7(e) is a view explaining a voltage to be applied to a lightdeflector.

FIG. 8 is a view explaining a schematic structure of a conventionalmagneto-optical disk.

FIG. 9 is a view explaining a schematic structure of anotherconventional magneto-optical disk.

DESCRIPTION OF THE EMBODIMENTS

The following description discusses a first embodiment of the presentinvention with reference to FIG. 1.

As illustrated in FIG. 1, a magneto-optical disk of this embodiment isprovided with concentric or spiral grooves 1 having an interruptedportion in each rotation. The interrupted portion forms a flat mirroredsection 3. The width (W_(G)) of each groove 1, the width (W_(L)) of aland 2 between the grooves 1, and the track pitch (P_(D)) are all equal.

The mirrored sections 3 have therein address information recorded in theform of pits 4a (a first series of pits), while portions of the lands 2near the mirrored sections 3 have therein address information recordedin the form of pits 4b (a second series of pits). Namely, the pits 4aand pits 4b are formed in different radial directions of themagneto-optical disk.

With this arrangement, information is recorded on the grooved tracks 1and tracks formed by lands 2. Whether light spot 6 is controlled tofollow the grooved tracks 1 or the land tracks 2 is easily selected byreversing the polarity of tracking signals. For example, the trackingsignals are generated by a push-pull method.

When the light spot 6 scans the grooved tracks 1, the addressinformation is retrieved from the pits 4a. On the other hand, when thelight spot 6 scans the land tracks 2, the address information isretrieved from the pits 4b.

As described above, in the magneto-optical disk of this embodiment, thepits 4a and pits 4b are formed in different radial directions so thatthey are not located next to each other. Thus, the light spot 6 is neverprojected on the pit 4a and pit 4b at the same time. This arrangementrestricts crosstalk, thereby providing accurate address information.

With the use of the magnetic super resolution effects, it is possible tomake the diameter of a recording domain 5 around 0.4 μm when recordinginformation. When the width of the track is 0.8 μm (i.e., the widths ofthe groove 1 and the land 2 are also set to 0.8 μm, respectively),recording and reproduction are easily performed. By reducing the trackpitch to a half of the conventional pitch of 1.6 μm, i.e., to 0.8 μm,the recording density is significantly improved while providing accurateaddress information.

Meanwhile, when laser light with a shorter wavelength is used for therecording and reproduction of information, it is possible to furtherreduce the track pitch. For instance, when laser light with a wavelengthof 458 nm is used instead of the laser light with a wavelength of 830nm, a track pitch, given by multiplying 0.8 μm by 458/830, is obtained,achieving almost doubled recording density.

According to this embodiment, in the case where the magneto-optical diskis divided into a plurality of sectors and the memory area thereof ismanaged by tracks and sectors, mirror sections 3 of a number equal tothe number of sectors are needed to be formed in each rotation of thegroove 1, and pits 4a and 4b are needed to be formed in each mirrorsection 3.

On the other hand, if the memory area of the magneto-optical disk ismanaged by a plurality of tracks, only one mirror section 3 is formedevery n (n>1) rotation of the groove 1, and the pits 4a and 4b areformed in each mirror section 3.

It is also possible to divide the magneto-optical disk into a pluralityof ring-shaped zones and to vary the number of sectors per track in eachzone.

The pits 4a are arranged either in the same radial direction ordifferent radial directions. The same is said for the pits 4b.

In order to obtain accurate address information or tracking signals, itis not desirable to arrange the pits 4b or the groove 1 adjacent to theinner edges (facing the center of the magneto-optical disk) of the pits4a or the outer edges (facing the periphery of the magneto-optical disk)thereof.

One of the reasons for this is that such an arrangement causes a crosstalk in address signals. Another reason is that, if the light spot 6scans the pit 4b when scanning a track on the land 2, the polarity ofthe tracking signal is inverted, causing instable tracking.

The following description discusses a second embodiment of the presentinvention with reference to FIG. 2. The members having the samestructure (function) as in the first embodiment are designated by thesame code and their description is omitted.

A significant difference between the magneto-optical disk of the firstembodiment and a magneto-optical disk of this embodiment is that addressinformation as pits 4b is recorded in portions of lands 2 far from themirrored sections 3 in this embodiment.

This arrangement further restricts crosstalk between the pits 4a andpits 4b, thereby providing more accurate address information.

The following description discusses a third embodiment of the presentinvention with reference to FIG. 3. The members having the samestructure (function) as in the above-mentioned embodiments aredesignated by the same code and their description is omitted.

Differently from the magneto-optical disks of the first and secondembodiments, grooved portions la adjacent to the pits 4b have a reducedwidth compared to that of the grooves 1 in a magneto-optical disk ofthis embodiment. Additionally, in this embodiment, the grooved portion1a is not necessarily connected to the groove 1.

When the widths of the groove 1 and land 2 are 0.8 μm, respectively, thegrooved portion 1a has a width between 0.4 and 0.5 μm.

As a result, the difference in the amount reflected light between lightreflected from a portion the land 2 having the pits 4b and lightreflected from a portion of the land 2 having no pit 4b becomes greaterthan those in the above-mentioned embodiments. It is therefore possibleto obtain more accurate address information from the pits 4b.

When seeking an improvement of the quality of signals from the pits 4b,the width of the grooved portion 1a is preferably reduced to, forexample, 0.3 to 0.4 μm. On the other hand, when seeking an improvementof the signal quality of magneto-optical signals from recording domainsrecorded on the grooves 1, the grooved portion 1a preferably has agreater width of, for example, 0.4 to 0.6 μm. Namely, when the groovedportion 1a has a width between 0.4 and 0.5 μm, both signals from thepits 4b and from the recording domains have satisfactory signal quality.

In the first to third embodiments, the width of the groove 1 is equal tothe width of the land 2. Therefore, when the track of the groove 1 andthe track of the land 2 are scanned with the light spot 6, the amount ofthe reflected light from the groove 1 is equal to that of the reflectedlight from the land 2. Namely, the strength of the signals obtained byscanning these tracks are substantially the same. Consequently, theprocessing circuit for the reproduced signal is simplified.

In order to obtain a strong track cross signal, the width of the of thegroove 1 and the width of the land 2 may be arranged different from eachother to some degree. The track cross signal represents a change in theamount of reflected light of the light spot 6 when it crosses the track.A tracking error signal represents a deviation of the light spot 6 fromthe center of the track 1. To access a target track, the movingdirection of the light spot 6 is detected based on a difference in phasebetween the track cross signal and the tracking error signal.

Although the strong track cross signal is obtained when the differencebetween the width of the groove 1 and that of the land 2 is great, thequality of the reproduced signal deteriorates.

For example, in the case where the sum of the width of the groove 1 andthe width of the land 2 is 1.6 μm (or the track pitch is 0.8 μm), thewavelength of the laser light is 780 nm and the numerical aperture ofthe objective lens is 0.55, if the width of the groove 1 or the land 2is less than 0.4 μm, the difference between the reflectance at the trackof the groove 1 and that at the track of the land 2 becomes greater.Namely, the amount of reflected light from the track of a narrower widthsignificantly decreases.

On the other hand, if the width of the groove 1 or the land 2 is between0.7 and 0.8 μm, a strong track cross signal is not obtained. In order toobtain appropriate reproduced signals and track cross signals, it isdesirable to arrange the width of the groove 1 or the land 2 within therange of 0.4 to 0.7 μm.

In general, when the width of the groove 1 or the land 2 is not greaterthan about 30 percent of the diameter of the light spot 6 (780nm/0.55×0.3=0.42 μm according to the above-mentioned example), thedifference between the reflectance at the track of the groove 1 and thatat the track of the land 2 becomes greater. Also, when the width of thegroove 1 or the land 2 exceeds about 45 percent of the sum of width ofthe groove 1 and the width of the land 2 or the twice the track pitch(1.6 μm×0.45=0.72 μm according to the above-mentioned example), thetrack cross signal is significantly weakened.

Thus, to obtain appropriate reproduced signals and track cross signals,it is desirable to arrange the width of the groove 1 and of the land 2not to be less than 30 percent of the diameter of the light spot 6 andnot to be greater than 45 percent of the twice the track pitch.

With reference to FIG. 4, the following description discusses a processof making a master of each of the three types of magneto-optical disksdescribed in the first through third embodiments.

Firstly, a photoresist 8 is applied to a surface of a quarts substrate 7as shown in FIG. 4(a). Secondly, laser light is converged on thephotoresist 8 so as to create desired patterns of grooves 1, pits 4a and4b on the surface thereof. After developing the photoresist 8, unwantedportions of the photoresist 8 are removed so that a photoresist 8acorresponding to the desired patterns of the grooves 1, pits 4a and 4bremains on the substrate 7 as shown in FIG. 4(b).

The photoresist 8a serves as a mask when dry-etching the substrate 7(see FIG. 4c). For example, CF₄ is used as etching gas. After etching,the photoresist 8a is removed as shown in FIG. 4(d) and a metal layer 9made of Ni is electroformed as shown in FIG. 4(e). Then, the metal layer9 is separated to obtain a stamper as shown in FIG. 4(f).

By molding plastic such as polycarbonate with the stamper, a substratewith the desired patterns of the grooves 1, pits 4a and 4b is obtained.When a recording medium is formed on the substrate, the magneto-opticaldisk is obtained.

FIG. 5 shows one example of a recording device used in an exposureprocess for creating the desired patterns of the grooves 1, pits 4a and4b with the photoresist 8.

The recording device has a laser light source 11a for the exposure ofthe photoresist 8, and a laser light source 11b for focusing anobjective lens 10. For example, argon laser is used as the laser lightsource 11a and He--Ne laser is used as the laser light source 11b.

Laser light from the laser light source 11a passes through a noisesuppressor 12 for reducing optical noise, is reflected by mirrors 19 and20, and then falls upon a beam splitter 21. The beam splitter 21 splitsthe laser light into two beams of light. One of the beams of light fallsupon a light modulator 18a, and the other falls upon a light modulator18b after being reflected by a mirror 24b. For example, acoustic opticalelements are used as the light modulators 18a and 18b. In this case,there is a need to place a convex lens 22 for convergence in front ofand behind each light modulator 18a or 18b.

The light beam from the light modulator 18a falls upon a light deflector23a and is then reflected at a right angle by the mirror 24a. And, thelight beam from the light modulator 18b falls upon a light deflector 23band then upon a half-wave plate 25, so that a plane of polarization isturned by 90 degrees. For example, elements capable of changing thetravelling direction of the light with the use of electro-opticaleffects or acoustic optical effects are used as the light deflectors 23aand 23b.

These light beams are joined by a polarizing prism 26 and then expandedto have an appropriate beam diameter a beam expander 27. After the beamshave been expanded, the beams are reflected by a bicolor mirror 15 andfall upon the objective lens 10. The objective lens 10 converges thebeams into light spots 31a and 31b, to be described later, on thephotoresist 8 on the substrate 7.

The light modulators 18a and 18b are controlled by drivers 28a and 28b,respectively, while the light deflectors 23a and 23b are controlled bydrivers 29a and 29b, respectively.

Meanwhile, the laser light from the laser light source 11b passesthrough a noise suppressor 12b for reducing optical noise, a beamsplitter 13, a quarter-wave plate 14, a bicolor mirror 15, and is thenconverged on the photoresist 8 on the substrate 7 by the objective lens10.

The reflected light is converged by the objective lens 10, passesthrough the bicolor mirror 15, the quarter-wave plate 14, and the beamsplitter 13. The light is then converged on a four-quadrantphotodetector 18 by an objective lens 16 and a cylindrical lens 17.Based on signals from the photodetector 18, focus servo signals aregenerated so that a focus servo system (not shown) drives the objectivelens 10 in a focussing direction. The objective lens 10 is thus alwaysfocused when the photoresist 8 on the substrate 7 is rotated by aspindle motor 30.

The following description discusses how the photoresist 8 is exposed inthe recording device with reference to FIG. 6.

Firstly, a d.c. voltage to be applied to the light deflectors 23a and23b by the drivers 29a and 29b and the setting angles of the mirrors 24aand 24b are adjusted so as to focus the light spots 31a and 31b at adistance equal to the track pitch onto a line extending in a radialdirection of the magneto-optical disk as shown in FIG. 6(a).

Then, the light intensity I₁ of the light spot 31a is controlled asshown in FIG. 6(b) by the driver 28a so that the light spot 31a isirradiated on the photoresist 8 to create the groove 1, pits 4a ,grooved portion 1a and groove 1 in this order from the left as shown inFIG. 6(a).

More specifically, when the photoresist 8 is exposed to have the patternof the grooves 1, the light intensity I₁ is set to high level P₁.Similarly, when the photoresist 8 is exposed to have the pattern of pits4a, the light intensity I₁ is set to low level P₄. And when thephotoresist 8 is exposed to have the pattern of the grooved portions 1a,the light intensity I₁ is set to the low level P₂. On the other hand,when the exposure of the photoresist 8 is not required, the lightintensity I₁ is set to zero. Thus, the size of the exposed area of thephotoresist 8 is controlled by varying the light intensity I₁.

When the photoresist 8 is exposed to create the pattern of pits 4bparallel to the grooves 1a as shown in FIG. 6(a), the light intensity I₂of the light spot 31b is controlled by the driver 28b as shown in FIG.6(c).

More specifically, when the photoresist 8 is exposed to create thepattern of pits 4b, the light intensity I₂ is set to low level P₃. Onthe other hand, when the exposure of the photoresist 8 is not needed,the light intensity I₂ is set to zero.

Another exposure method employed by the recording device is explainedbelow with reference to FIG. 7.

A difference between the method of the above-mentioned embodiment andthat of this embodiment is that the grooves 1 are formed by two lightspots 31a and 31b with the method of this embodiment.

In order to project the light spots 31a and 31b at a distance equal to ahalf of the track pitch onto a line extending in a radial direction ofthe magneto-optical disk as illustrated in FIG. 7(a), the d.c. voltageto be applied to the light deflectors 23a and 23b by the drivers 29a and29b and the setting angle of the mirrors 24a and 24b are adjusted.

Then, in order to create a half portion (upper half in the drawing) ofthe groove 1, the pits 4a, the grooved portion 1b and the half portionof the groove 1 in this order from the left, the light spot 31a isprojected onto the photoresist 8 while controlling the intensity I₁thereof as shown in FIG. 7(b) by the driver 28a.

Namely, when the photoresist 8 is exposed to create the pattern of thehalf portion of the grooves 1, the light intensity I₁ is set to levelP₅. When the photoresist 8 is exposed to create the pattern of the pits4a, the light intensity I₁ is set to level P₇. When the photoresist 8 isexposed to create the pattern of the grooved portion 1b, the lightintensity I₁ is set to level P₆. And, when the exposure of thephotoresist 8 is not required, the light intensity I₁ is set to zero.Thus, by varying the light intensity I₁ , the size of the exposed areaof the photoresist 8 is controlled.

Meanwhile, when the photoresist 8 is exposed to create the patterns ofthe pits 4a and the grooved portions 1b, the voltage to be applied tothe light deflector 23a by the driver 29a is shifted by V₁ and the lightspot 31a is centralized on the groove 1 in a cross direction.

On the other hand, in order to create a half portion (lower half in thedrawing) of the groove 1, and pits 4b parallel to the grooved portion 1bas shown in FIG. 7(a), the light spot 31b is projected onto thephotoresist 8 while controlling the intensity I₂ thereof by the driver28b as shown in FIG. 7(c).

More specifically, when the photoresist 8 is exposed to create thepattern of the half portion of the grooves 1, the light intensity I₁ isset to level P₅. When the photoresist 8 is exposed to create the patternof the pits 4b, the light intensity I₂ is set to level P₉. And, when theexposure of the photoresist 8 is not required, the light intensity I₁ isset to zero.

When the photoresist 8 is exposed to create the patterns of the pits 4band the grooved portions 1a, a voltage to be applied to the lightdeflector 23b by the driver 29b is shifted by V₂ as shown in FIG. 7(e)and the light spot 31b is centralized on the land 2 in a crossdirection.

With this method, when the width of the grooved portion 1b and thediameters of the pits 4a and 4b are respectively equal to a half of thewidth of the groove 1, it is possible to set P₅, P₆, P₇ and P₉ to havethe same value, the light intensities I₁ and I₂ of the light spots 31aand 31b are easily set to two levels. As a result, the control of thelight spots 31a and 31b becomes easier compared to those by theabove-mentioned methods.

The above description discusses the exposure process of the photoresist8 in the recording device by using, for example, the magneto-opticaldisk of the third embodiment. However, this process is also applied tothe magneto-optical disks of the first and second embodiments.

Magneto-optical disks and the method of manufacturing themagneto-optical disks are explained in the above-mentioned embodiments.This invention is also applicable to a wide range of optical diskshaving address information in the form of pits 4a and 4b and to methodsof manufacturing these disks.

The invention being thus described, it will be obvious that the same maybe varied in many ways. Such variations are not to be regarded as adeparture from the spirit and scope of the invention, and all suchmodifications as would be obvious to one skilled in the art are intendedto be included within the scope of the following claims.

What is claimed is:
 1. An optical disk comprising: concentric or spiralgrooves, said grooves having an interrupted portion in each rotation,and a plurality of land portions formed between the grooves;a firstseries of pits recorded in an interrupted portion as addressinformation; and a second series of pits recorded in a portion of landas address information, the portion of said land and the interruptedportion of said groove being located in different radial directions. 2.The optical disk according to claim 1,wherein a width of one of saidland portions between said grooves is equal to a width of said groove.3. The optical disk according to claim 1,wherein said second series ofpits is formed in a portion of said land portion located at a positiondistal to the interrupted portion of said groove.
 4. The optical diskaccording to claim 1,wherein the width of said groove becomes smallerproximate to the interrupted portion of said groove, and said secondseries of pits are formed in one or more land portions located betweensaid grooves with a smaller width.
 5. The optical disk according toclaim 1, wherein said optical disk is a magneto-optical disk, andinformation is recorded and reproduced on/from tracks in the form ofsaid grooves and lands.
 6. An optical disk comprising:concentric orspiral grooves having interrupted portions and a plurality of landportions formed between the grooves; a first series of pits recorded asaddress information in said interrupted portion of said grooves; and asecond series of pits recorded as address information in a portion ofland, the portion of said land and the interrupted portion of saidgroove being located in different radial directions, wherein a width ofeach of said land portions between said grooves or a width of saidgroove is not less than 30 percent of a diameter of a light spotprojected to reproduce said address information from said first andsecond series of pits but not greater than 45 percent of a sum of thewidths of said land and said groove.
 7. An optical diskcomprising:concentric or spiral grooves having interrupted portions; amagneto-optical recording medium layer, formed on a side of a substratehaving said grooves, for enabling information to be recorded thereon bymagnetic super resolution effects, a first series of pits recorded asaddress information on a line extending from the interrupted portions ofsaid grooves; and a second series of pits recorded as addressinformation in a portion of land located between said grooves, theportion of said land and the interrupted portion of said groove beinglocated in different radial directions; wherein information is recordedon said magneto-optical recording medium layer on said grooves and landswith magnetic super resolution effects, and said address information isreproduced from said first and second series of pits.
 8. The opticaldisk according to claim 4,wherein at said smaller width the grooves havea width of between about 0.4 and 0.6 μm.
 9. The optical disk accordingto claim 4,wherein at said smaller width the grooves have a width ofbetween about 0.4 and 0.5 μm.
 10. The optical disk according to claim4,wherein at said smaller width the grooves have a width of betweenabout 0.3 and 0.4 μm.
 11. The optical disk according to claim 1,whereinthe first series of pits and the second series of pits are located indifferent radial directions.
 12. The optical disk according to claim6,wherein the first series of pits and the second series of pits arelocated in different radial directions.
 13. The optical disk accordingto claim 7,wherein the first series of pits and the second series ofpits are located in different radial directions.
 14. An optical diskcomprising:concentric or spiral grooves, said grooves having at leastone interrupted portion, and a plurality of land portions formed betweenthe grooves; a first series of pits recorded in an interrupted portionas address information; and a second series of pits recorded in aportion of land as address information, the portion of said land and theinterrupted portion of said groove being located in different radialdirections.
 15. The optical disk according to claim 14,wherein the widthof said groove becomes smaller proximate to the interrupted portion ofsaid groove, and said second series of pits are formed in one or moreland portions located between said grooves with a smaller width.
 16. Theoptical disk according to claim 15,wherein at said smaller width thegrooves have a width of between about 0.4 and 0.6 μm.
 17. The opticaldisk according to claim 15,wherein at said smaller width the grooveshave a width of between about 0.4 and 0.5 μm.
 18. The optical diskaccording to claim 15,wherein at said smaller width the grooves have awidth of between about 0.3 and 0.4 μm.
 19. The optical disk according toclaim 14,wherein said optical disk is a magneto-optical disk, andinformation is recorded and reproduced on/from tracks in the form ofsaid grooves and lands.
 20. The optical disk according to claim14,wherein the first series of pits and the second series of pits arelocated in different radial directions.
 21. A magneto-optical diskcomprising:discontinuously arranged concentric or spiral elongatedgrooves; an interrupted portion formed between grooves among saidgrooves, which are located next to each other in a circular direction;concentric or spiral land portions located at least adjacent to and inparallel with said grooves; a first series of pits recorded as addressinformation in said interrupted portion; a second series of pitsrecorded as address information in said land portion, wherein saidsecond series of pits is formed in a portion of said land portionlocated in a radial direction different from a radial direction in whichthe interrupted portions of one or more said grooves next to said landportion are located.
 22. The disk according to claim 21,wherein thefirst series of pits and the second series of pits are located indifferent radial directions.
 23. The optical disk according to claim 21,wherein said optical disk is a magneto-optical disk.